1. Field of the Invention
The present invention relates to a technology of operating on image data in an image compression process, an image regeneration process, and an image quality switching process.
2. Description of the Related Art
A digital camera is generally known as a device capable of shooting a subject, displaying a shot image, and recording the shot image.
With the digital camera, a subject image is input as an electric signal by an optoelectronic conversion by an image pickup device such as a CCD (charge coupled device), and various processes such as color signal processing, etc. and an analog-to-digital conversion are performed on the input subject image. Thus, the generated subject image can be processed as digital data, and digital processing such as image compression and decompression is performed. When the subject image is recorded, it can be recorded to a built-in memory of a digital camera or a recording medium (for example, CompactFlash®, SmartMedia®, etc.) removable from a digital camera. When the subject image is displayed, it can be displayed on a display unit (for example, an LCD, etc.) configured in a digital camera.
Furthermore, in the above-mentioned digital camera, the subject image can be recorded in the recording unit of an external communications device, or displayed on the display unit of an external communications device by combining and using external communications devices having large-capacity recording units and display units.
The technology of recording the subject image in the recording unit of the external communications device has been disclosed as transferring captured image data to an external device having a large-capacity recording medium by a wireless communications unit, and clearing the transferred image data from the built-in memory of a camera in the Japanese Patent Application Laid-open No. 11-284894.
Furthermore, the technology of displaying a subject image on the external communications device has been disclosed as capable of transmitting, to a remote control device, a subject image captured by a digital camera before a shutter operation (transmitting the above-mentioned release signal) from a remote control device by using the well-known technology according to the release signal from the remote control device, and checking the subject image in advance on the display unit of the remote control device in the Japanese Patent Application Laid-open No. 5-72608.
Furthermore, the technology of displaying a subject image on the external communications device has been disclosed as improving the communications speed of the subject image by performing a binarization process on the subject image when a captured subject image is transmitted to the external communications device in the Japanese Patent Application Laid-open No. 11-174576.
In the above-mentioned digital camera, the above-mentioned compression process is performed on a digitized subject image.
The technology of obtaining the optimum compression rate for each subject image in the compression process has been disclosed as determining a quantization parameter based on two trial compression processes on the subject image, and performing a real compression process on the subject image according to the determined quantization parameter in the U.S. Pat. No. 5,594,554.
FIG. 1A is a timing chart for explanation of the technology.
FIG. 1A shows the timing chart of the trial compression and the real compression performed on the fetched input image (subject image) based on the vertical synchronizing signal VD.
That is, as shown in the timing chart in FIG. 1A, the technology performs two trial compression processes on the input image fetched as image data, obtains a quantization parameter and the amount of coded data for each of the trial compression processes, computes a target quantization parameter based on the obtained quantization parameter and the amount of coded data, performs a real compression process on each input image based on the computed target quantization parameter.
As another technology of optimizing the compression rate for each subject image when the above-mentioned compression process is performed, a method of obtaining a quantization parameter by performing a trial compression process only on the leading frame of an input image, and performing the compression process on the subsequent frames using the quantization parameter used in the compression process on the leading frame is suggested.
FIG. 1B is a timing chart for explanation of the method.
As shown in FIG. 1B, two trial compression processes are performed on the leading frame of an input image, a real compression process is performed on the leading frame according to the target quantization parameter similarly obtained as in the trial compression process, and a real compression process is performed on each image input subsequently using the same quantization parameter.
Thus, the compressed subject image is displayed on the display unit of a digital camera or the display unit of an external communications device, or recorded in the recording memory built in a digital camera, a removable recording medium, or a recording unit of an external communications device.
Additionally, at a regeneration designation, a digital camera reads a subject image recorded to the recording medium or the recording unit of an external communications device, and performs a compression/decompression process, etc. on the read subject image, thereby regenerating an image on the display unit of the digital camera.
The larger the amount of the data of a subject image, the longer the time required from the regeneration designation on the subject image to the display of the subject image on the display unit (hereinafter referred to as a “regeneration start waiting time” in the present specifications).
The moving picture data which has recently been widely used with the remarkable progress of hardware specifically requires a longer regeneration start waiting time.
The technology of shortening the regeneration start waiting time for moving picture data has been disclosed as recording in advance a scene or a cut of moving picture data as a segmentation unit, and the regeneration starting position of each unit as an index, and reading the address information about a part of data of the moving picture data and the subsequent moving picture data recorded in the recording unit in the buffer memory, thereby immediately regenerating a desired scene by specifying the starting address from the above-mentioned index recorded in advance.
Thus, the processes have been performed corresponding to the image data in the image compression process, the image regeneration process, the image quality switching process, etc.